1. Field of the Invention
The present invention relates to a liquid level detecting apparatus for detecting that the level of a liquid has attained a predetermined level.
2. Description of the Prior Art
An apparatus of the above type is known in the art in which the level of a liquid to be measured is detected by means of a float including a magnet and one or more reed switches which are opened and closed by the magnet. However, this conventional detecting method requires the use of a magnet having a sufficient magnetic force for opening and closing the reed switches and a float of a size sufficient to provide the required buoyancy to float the magnet. Particularly, this detecting method is disadvantageous in that since this method utilizes the magnetic attractive force which acts between the reed switches and the magnet, it is nearly impossible to realize the reduction in the size and weight of the apparatus.
Japanese Utility Model Laid-Open (publication) No. 50-31961 discloses a liquid level sensor employing an oscillator circuit. More specifically, the sensor comprises an oscillator circuit, a guide rod accommodating therein the oscillator coil of the oscillator circuit and a float movable along the guide rod in accordance with the liquid level, and the secondary winding of the oscillator coil consisting of a short-circuit conductor is provided on the float, thereby permitting the detection of the level of liquid. While this device has many advantages, it is also disadvantageous in that since the presence of the output signal of the oscillator circuit produced by the movement of the float is discriminated in accordance with the signal rectified by a rectifier circuit including, for example, a capacitor, diodes, resistor, etc., the number of component parts used in the device is increased.